Ive moved the trafo out of the 19" 2U rackmount box, and the problem is still there.

Its leaving me with only one more possibilty... supply ripple.
The weird thing is that this Amp never had a problem with noise until about 1 week ago.
Surely the 4 10,000uF caps smoothing the power after the bridge-rect cant degrade that quickly.

If you hear the sound coming out of the speaker then your transformer is not vibrating mechanically.

Are you hearing a 50-60 hz hum (line frequency) or 100-120 hz sound (capacitor charging) or other higher frequency noise (maybe rf or other hash on you mains)? Do all of your channels have the problem or some subset?

If what you are saying is that you've done the star grounding and still have hum somewhere in you amp, I think it is more likely that you still have a gound loop problem rather than a transformer problem. Check to see if it is a problem with the source you have connected. Try feeding it with a baterry powered CD player or something else that does not connect to mains power or ground. If the hum goes away, then your problem is a loop between your amp and the mains connected input device.

If you still have a hum with a battery input device check to make sure your line level input is shielded and/or physically separated from mains voltage wires and away from diode bridges if possible. Make sure all you connections to power and grounds are solid.

Make sure your connection to power are as far away, physically from the diode bridges as possible. I.E. pick up your V+ and V- from the filter capacitor that is farthest from the bridge, not at the bridge. High current charging current between the bridge and capacitors can cause 100-120 hz noise.

Is your transformer a Toroid or a square El? If you have tried your transformer from a foot or more away and you have tried various physical orientations you can be pretty sure you are not getting hum coupled magnetically.

Are you hearing a 50-60 hz hum (line frequency) or 100-120 hz sound (capacitor charging) or other higher frequency noise (maybe rf or other hash on you mains)? Do all of your channels have the problem or some subset?

All channels have the hum.
Im not sure if its 50Hz or 100.

Quote:

If what you are saying is that you've done the star grounding and still have hum somewhere in you amp, I think it is more likely that you still have a gound loop problem rather than a transformer problem. Check to see if it is a problem with the source you have connected. Try feeding it with a baterry powered CD player or something else that does not connect to mains power or ground. If the hum goes away, then your problem is a loop between your amp and the mains connected input device.

Its not a ground loop (well to external sources anyway).
I can ground the input to the channels and itll still hum.

Quote:

Make sure your connection to power are as far away, physically from the diode bridges as possible. I.E. pick up your V+ and V- from the filter capacitor that is farthest from the bridge, not at the bridge. High current charging current between the bridge and capacitors can cause 100-120 hz noise.

I am doing this already.

Quote:

Is your transformer a Toroid or a square El? If you have tried your transformer from a foot or more away and you have tried various physical orientations you can be pretty sure you are not getting hum coupled magnetically.

To MVP : If you will look at Per - Anders home pages, you will see there too my amp PA - 03, where you can to take inspiration about correct grounding. This amp is quite silent, no noise, no hum. It is with LM 4780, but it is the same as with LM 3886 .